1. Field of the Invention
The present invention relates to an audio information processing apparatus, an audio information processing method, and a method of recording audio information on a recording medium, which are suitably arranged for a remaster apparatus or the like, for converting audio data recorded on a so-called compact disk (disc) (CD) into audio data for a video disk (disc) (digital video disk or digital versatile disk:DVD) which requires higher tone quality to remaster the audio data and, more particularly, to an audio information processing apparatus, an audio information processing method, and a method of recording audio information on a recording medium which generate harmonic sound on the basis of coded audio information and add the harmonic sound to original audio information as a predetermined band component to design extension or the like of the band of the original audio information.
2. Description of Related Art
It has been performed that an audio signal input as an analog signal is subjected to a sampling process at a predetermined sampling frequency and subjected to a quantization process to form coded audio data whose band is limited, and the audio data is recorded on a recording medium such as an optical disk. As a typical recording medium on which the audio data is recorded, a so-called compact disk (CD) is known. On the compact disk, 16-bit audio data which is subjected to a sampling process at a sampling frequency of 44.1 kHz to be formed is recorded.
A so-called digital video disk (DVD) obtained in the following manner is known. That is, image information including a lot of audio information and a lot of video information amount is highly efficiently compressed and coded by a moving picture compression processing apparatus such as an MPEG apparatus (MPEG: moving picture experts group), and the image information is recorded on an optical disk having a size (12-cm diameter) equal to that of a compact disk. The digital. video disk has spread. On the digital video disk, 24-bit (or 20-bit) audio data formed by an analog audio signal is subjected to a sampling process at a sampling frequency of 96 kHz (or 88.2 kHz which is expected to be added as a new standard) is recorded.
For example, when an analog audio signal has a frequency band up to 48 kHz as indicated by a dotted line in FIG. 1, the analog audio signal is subjected to a sampling process at a sampling frequency of 44.1 kHz for a compact disk to be converted into 16-bit audio data. In this case, the audio data has a frequency characteristic in which a frequency band of 22.05 kHz or more is removed as indicated by an alternate long and short dash line in FIG. 1. In contrast to this, when an analog audio signal is subjected to a sampling process at a sampling frequency of 96 kHz for a digital video disk to be converted into 24-bit audio data, audio data having a frequency band up to 48 kHz can be formed like an analog audio signal as indicated by a solid line in FIG. 1.
Here, when an analog audio signal is converted into digital audio data, the resolution of the digital audio data depends on the number of quantization bits, and the frequency band of the digital audio data depends on a sampling frequency. For this reason, even if 16-bit data formed by performing a sampling process at a sampling frequency of 44.1 kHz for a compact disk is subjected to an over-sampling process at a sampling frequency of, e.g., 88.2 kHz, the 16-bit original audio data does not include sound having the frequency band of 22.05 kHz or more. For this reason, the frequency band of the audio data itself after the over-sampling process does not change.
Theoretically, the hearing sense of human being is limited to about 20 kHz. However, it is. known that sound having a frequency band of 20 kHz or more and serving as the difference between the frequency band of a compact disk and the frequency band of a digital video disk; as indicated by a diagonal line in FIG. 1 brings a rich hearing sense, though the sound cannot be heard.
For this reason, a technique in which the waveform of original audio information is shaped to emphasize or add harmonic and to record/reproduce rich sound is popularly studied. A technique for obtaining a non-linear waveform by using a conversion table is disclosed in Japanese Patent Application Laid-Open No. 5-127672; a technique for further performing a differential operation to form a complex nonlinear waveform is disclosed in Japanese Patent Application Laid-Open No. 7-175478; a technique-for performing a non-linear process after an over-sampling process to form harmonic is disclosed in Japanese Patent Application Laid-Open No. 7-66687; and a technique for performing a non-linear process after an over-sampling process to extract a wide-band component and adding the wide-band component to original audio information to form wide-band audio information is disclosed in Japanese Patent Application Laid-Open No. 7-236193.
However, since a conventional technique for emphasizing or adding harmonic is designed to use a conversion table for a non-linear process, a differential circuit, or a cube circuit, costs increase, and poor productivity is obtained because of a large circuit scale and a large, chip size. In recent years in which price buster and downsizing are demanded, it is an important problem to provide a compact and high-performance audio information processing apparatus.
It is an object of the present invention to provide an audio information recording method, an audio information recording apparatus, and a method of recording audio information on a recording medium in which audio information having a narrow frequency band can be converted into audio information having a wide frequency band with a compact, simple, and low-price circuit arrangement.
It is another object of the present invention to provide a code information processing method, a code information processing apparatus, and a method of recording code information on a recording medium in which code information having a narrow frequency band can be converted into code information having a wide frequency band with a compact, simple, and low-price circuit arrangement without using a special conversion table for a non-linear process and arranging a cube circuit or the like.
To achieve the object of the present invention, from the first aspect, there is provided an audio information processing method according to the present invention comprising the steps of: comparing audio information supplied from the outside every predetermined sample; detecting maximal values and minimal values of waveforms of the audio information; detecting an interval extending from a maximal value to a minimal value detected in the above step and an interval extending from the minimal value to a maximal value; forming a predetermined band component corresponding to the interval extending from the maximal value to the minimal value or the interval extending from the minimal value to the maximal value detected in the above step on the basis of the audio information supplied from the outside; and performing an addition process, a subtraction process, or an addition-subtraction process to the predetermined band components with respect to the audio information supplied from the outside at a timing corresponding to the interval extending from the maximal value to the minimal value or the interval extending from the minimal value to the maximal value detected in the above step to add the predetermined band components to the audio information supplied from the outside.
Further, from the second aspect, there is provided an audio information processing apparatus according to the present invention comprising: comparison means for comparing audio information supplied from the outside every predetermined sample; maximal/minimal value detection means for detecting maximal values and minimal values of waveforms of the audio information; interval detection means for detecting an interval extending from a maximal value to a minimal value detected by the maximal/minimal value detection means and an interval extending from the minimal value to a maximal value; band component forming means for forming a predetermined band component corresponding to the interval extending from the maximal value to the minimal value or the interval extending from the minimal value to the maximal value detected by the interval detection means on the basis of the audio information supplied from the outside; and band component addition means for performing an addition process, a subtraction process, or an addition-subtraction process to the predetermined band components formed by the band component forming means with respect to the audio information supplied from the outside at a timing corresponding to the interval extending from the maximal value to the minimal value or the interval extending from the minimal value to the maximal value detected by the interval detection means to add the predetermined band components to the audio information supplied from the outside and to output the resultant audio information.
The audio information processing method and the audio information processing apparatus form the predetermined band components corresponding to the interval extending from the maximal value to the minimal value of the audio information or the interval extending from the minimal value to the maximal value. The predetermined band components are subjected to an addition process, a subtraction process, or an addition-subtraction process with respect to the audio information supplied from the outside at timings corresponding to the intervals to design extension of the frequency band of the audio information. In this manner, the extension of the frequency band can be designed by a simple process including only addition and subtraction. Therefore, the audio information processing method and the audio information processing apparatus according to the present invention can convert audio information having a narrow frequency band into audio information having a wide frequency band with a compact, simple, and low-price circuit arrangement.
Further, from the third aspect, there is provided a method of recording audio information on a recording medium according to the present invention wherein audio information generated by the audio information processing method is recorded on a predetermined recording medium.
The method of recording audio information on a recording medium as described above forms a predetermined band component corresponding to the interval extending from the maximal value to the minimal value of the audio information or the interval extending from the minimal value to the maximal value. The predetermined band component is subjected to an addition process, a subtraction process, or an addition-subtraction process with respect to audio information supplied from the outside at a timing corresponding to the interval to design extension of the frequency band of the audio information, and the audio information is recorded on a predetermined recording medium. In this manner, the extension of the frequency band can be designed by a simple process including only addition and subtraction, and the audio data can be recorded on a desired recording medium. Therefore, the method of recording audio information on a recording medium according to the present invention can convert audio information having a narrow frequency band into audio information having a wide frequency band with a compact, simple, and low-price circuit arrangement to record the resultant audio information on a recording medium.
Moreover, from the fourth aspect, there is provided a code information processing method according to the present invention comprising the steps of: comparing code information generated by sampling a waveform signal every predetermined sample; detecting a maximal sample point and a minimal sample point of the code information; detecting a before sample point and an after sample point respectively separated from the maximal sample point and the minimal sample point detected in the above step by a predetermined time; setting levels of the before sample point and the after sample point; connecting, of a maximal sample point and a minimal sample point which are adjacent to each other on time base, the after sample point at a before maximal sample point or a before minimal sample point to the before sample point at an after minimal sample point or a maximal sample point with a line; generating waveform information having a predetermined shape from the line obtained in the above step; extracting a predetermined frequency band component of the waveform information having the predetermined shape; and adding the predetermined frequency band component extracted in the above step to the code information.
Further, from the fifth aspect, there is provided a code information processing apparatus according to the present invention comprising: comparison means for comparing code information generated by sampling a waveform signal every predetermined sample; maximal/minimal sample point detection means for detecting a maximal sample point and a minimal sample point of the code information; before/after sample detection means for detecting a before sample point and an after sample point respectively separated from the detected maximal sample point and the detected minimal sample point by a predetermined time; level setting means for setting levels of the before sample point and the after sample point; line operation means for connecting the after sample point at a before maximal sample point or a before minimal sample point of a maximal sample point and a minimal sample point which are adjacent to each other on time base to the before sample point at an after minimal sample point or an after maximal sample point of the adjacent maximal and minimal sample points, with a line; trapezoidal waveform information generation means for generating waveform information having a predetermined shape from the line; frequency component extraction means for extracting a predetermined frequency band component of the waveform information having the predetermined shape; and addition means for adding the extracted predetermined frequency band component to the code information.
In the code information processing method and the code information processing apparatus according to the present invention, waveform information having a predetermined shape is generated from code information, and a predetermined frequency band component is generated from the waveform information having the predetermined shape. The predetermined frequency band component is added to the code information to design extension of the frequency band of the code information. In this manner, extension of the frequency band of the code information is realized by a compact, simple, and low-price circuit arrangement. In particular, by using audio information having a narrow frequency band as code information, the audio information having the narrow band is converted into audio information having a wide frequency band with a compact, simple, low-price circuit arrangement.
Further, from the sixth aspect, there is provided a method of recording code information on a recording medium according to the present invention wherein code information generated by the code information processing method is recorded on a predetermined recording medium.
In the method of recording code information on a recording medium according to the present invention, waveform information having a predetermined shape is generated from code information, and a predetermined frequency band component is generated from the waveform information having the predetermined shape. The predetermined frequency band component is added to the code information to design extension of the frequency band of the code information, and the code information whose frequency band is extended is recorded on a predetermined recording medium. In this manner, extension of the frequency band can be designed by a simple process including only addition and subtraction, and a predetermined recording medium on which code information whose frequency band is extended is recorded can be formed. The recording method can be realized with a compact, simple, and low-price circuit arrangement. In particular, by using audio information having a narrow frequency band as code information, the audio information having the narrow band can be converted into audio information having a wide frequency band with a compact, simple, and low-price circuit arrangement, and the audio information having the wide frequency band can be recorded on a recording medium.
More specifically, in the code information processing method, the code information processing apparatus, and the method of recording code information on a recording medium according to the present invention, a trapezoidal process is performed from a maximal sample point and a minimal sample point with respect to the change in waveform of code information, thereby generating a non-linear signal. In other words, according to the present invention, a harmonic component is extracted as a predetermined frequency band from a trapezoidal waveform generated from code information, and the harmonic component is added to the original code information, so that the band is extended by using the harmonic component as a component out of the frequency band of the code information.